1. Field of the Invention
The invention relates to a control device and method for a variable valve mechanism. More specifically, the invention relates to a control device for a variable valve mechanism that changes the operating characteristic of at least one of an intake valve and an exhaust valve in an internal combustion engine.
2. Description of the Related Art
Japanese Patent Application Publication No. JP-A-2004-183591 describes a control device for an internal combustion engine with a variable valve mechanism. When the actuator that drives the variable valve mechanism of the internal combustion engine overheats, the control device fixes the valve lift at the maximum value, and controls the amount of intake air using only a throttle valve, to stop the and suppress the overheating of the actuator. After the temperature of the actuator has decreased, the normal control resumes.
However, if the valve lift is fixed at the maximum value immediately after it is determined that the actuator overheats, the amount of intake air suddenly increases. As a result, a driver may feel vibrations (torque shock) due to the change in engine torque. Also, if the valve lift is suddenly set to an optimum value instead of the maximum value when the normal control is resumed, the driver may feel a torque shock.
The above-described patent publication does not describe any control for preventing the torque shock.